How tough is their group? Billed as ‘Wenger’s nightmare’ it is among the very toughest. Dortmund are the best side, Napoli have strengthened after selling Edinson Cavani and Marseille – with big Andre-Pierre Gignac up-front – are no pushover.

Biggest strength Arsene Wenger himself. For 16 years, Arsenal have qualified for the Champions League and have always made it through. Jack Wilshere needs to impose himself.

Biggest weakness The signing of Mesut Ozil was impressive but what happens if Olivier Giroud gets injured?

Key fixture A win over Napoli at home would fuel belief.

Key stat 1 The only manager with more Champions League experience than Wenger is Sir Alex Ferguson.

How tough is their group?Celtic are in the only section composed solely of former winners. Neil Lennon’s players cannot aspire to that status but they were last season’s surprise package when they beat Barcelona.

Biggest strength Celtic Park on a European night is a phenomenon. Barca lost there last year and Milan suffered the same fate in 2007.

Biggest weakness Central defence was ruthlessly exposed last year. Kelvin Wilson’s departure is a loss and replacement Steve Mouyokolo has ruptured his Achilles.

Key fixture The games against Ajax should decide third place.

Key stat 22 Celtic have lost 22 of their last 24 away games in the Champions League.